| 1. |
- Goto, Ken, et al.
(författare)
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Halide vapor phase epitaxy of Si doped beta-Ga2O3 and its electrical properties
- 2018
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 666, s. 182-184
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Tidskriftsartikel (refereegranskat)abstract
- Silicon doped homoepitaxial films were grown on beta-gallium oxide (001) substrates by halide vapor phase epitaxy using gallium monochloride, oxygen and silicon tetrachloride gases as precursors. It was confirmed that the n-type carrier density at room temperature was almost equal to the doped silicon concentration, which was controlled in the range of 10(15) to 10(18) cm(-3). In the doped film with the carrier density of 1x10(16) cm(-3), the activation energy and the mobility at room temperature were 45.6 meV and 145 cm(2)/V.s, respectively. The carrier scattering mechanism in the low carrier density film was dominated by optical phonon scattering with the phonon energy of 33 meV. These results suggest that the doped homoepitaxial film grown by halide vapor phase epitaxy is a high quality film with good crystallinity comparable to bulk crystals.
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| 2. |
- Goto, Ken, et al.
(författare)
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Study of Dislocations in Homoepitaxially and Heteroepitaxially Grown AlN Layers
- 2020
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Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 217:24
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Tidskriftsartikel (refereegranskat)abstract
- Dislocation densities in AlN layers grown on c-plane sapphire and physical vapor transport-grown AlN (PVT-AlN) (0001) substrates, by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE), respectively, are evaluated from the density of etch pits formed in sodium hydroxide (NaOH)/potassium hydroxide (KOH) eutectic heated to 450 degrees C. In the heteroepitaxial layers grown by MOVPE on the sapphire substrates, etch pits with different sizes are formed. Cross-sectional transmission electron microscopy (TEM) observations reveal that the large, medium, and small pits, with densities of 1.4 x 10(6), 2.6 x 10(7), and 6.9 x 10(9) cm(-2), respectively, correspond to screw, mixed, and edge dislocations, respectively. In contrast, in the homoepitaxial layers grown by HVPE on the PVT-AlN substrates, only one kind of etch pit with uniform size corresponding to the edge dislocations is formed with a density of 10(3)-10(4) cm(-2). Cross-sectional TEM observation confirms that the edge dislocations in the homoepitaxial layer propagate from the substrate through the interface, which indicates that the dislocation density does not increase during homoepitaxial growth by HVPE. The HVPE-AlN homoepitaxial layers grown on the PVT-AlN substrates are found to have very low dislocation density.
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| 3. |
- Higashiwaki, Masataka, et al.
(författare)
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Current Status of Gallium Oxide-Based Power Device Technology
- 2015
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Ingår i: 2015 IEEE COMPOUND SEMICONDUCTOR INTEGRATED CIRCUIT SYMPOSIUM (CSICS). - : IEEE. - 9781479984947
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Konferensbidrag (refereegranskat)abstract
- Gallium oxide (Ga2O3) possesses excellent material properties especially for power device applications. It is also attractive from an industrial viewpoint since large -size, high quality wafers can be manufactured by using simple methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this report, we describe the recent progress in development on fundamental technologies for Ga2O3 devices, covering wafer production from melt -grown bulk single crystals, homoepitaxial thin-film growth by halide vapor phase epitaxy, as well as device processing and characterization of metal -oxide -semiconductor field-effect transistors and Schottky barrier diodes.
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| 4. |
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| 5. |
- Higashiwaki, Masataka, et al.
(författare)
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Temperature-dependent capacitance-voltage and current-voltage characteristics of Pt/Ga2O3 (001) Schottky barrier diodes fabricated on n(-)-Ga2O3 drift layers grown by halide vapor phase epitaxy
- 2016
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 108:13, s. 133503-
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the temperature-dependent electrical properties of Pt/Ga2O3 Schottky barrier diodes (SBDs) fabricated on n(-)-Ga2O3 drift layers grown on single-crystal n(+)-Ga2O3 (001) substrates by halide vapor phase epitaxy. In an operating temperature range from 21 degrees C to 200 degrees C, the Pt/Ga2O3 (001) Schottky contact exhibited a zero-bias barrier height of 1.09-1.15 eV with a constant near-unity ideality factor. The current-voltage characteristics of the SBDs were well-modeled by thermionic emission in the forward regime and thermionic field emission in the reverse regime over the entire temperature range. (C) 2016 AIP Publishing LLC.
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| 6. |
- Hirasaki, Takahide, et al.
(författare)
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Growth of thick and high crystalline quality InGaN layers on GaN (000(1)over-bar) substrate using tri-halide vapor phase epitaxy
- 2016
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Ingår i: Journal of Crystal Growth. - : ELSEVIER SCIENCE BV. - 0022-0248 .- 1873-5002. ; 456, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- The growth of thick InGaN layers on free-standing GaN (000 (1) over bar substrates was studied using tri-halide vapor phase epitaxy. It was found that high-indium-content InGaN can be grown under higher InCl3 input partial pressure at higher growth temperature, which allows the fabrication of a high crystalline quality InGaN layer with a smooth surface morphology. Using the growth conditions of high InCl3 input partial pressure and high growth temperature, crack- and droplet-free InGaN layers with a thickness of over 10 mu m and with an indium fraction of 0.05 were successfully grown. Although the surface showed many hillocks, the number of hillocks was reduced upon growth of thicker InGaN layers. Photoluminescence measurements confirm that thick InGaN layers could be successfully grown without degradation of the crystalline quality. (C) 2016 Elsevier B.V. All rights reserved.
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| 7. |
- Hirasaki, Takahide, et al.
(författare)
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Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:5, s. 05FA01-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical properties were affected by NH3 input partial pressure. As shown in thermodynamic analyses, the indium content increased due to an increase in the driving force for InN deposition caused by increased NH3 input partial pressure. In addition, the deep level emission around 2.1 eV in photoluminescence measurements drastically decreased at higher NH3 input partial pressures. Ab initio calculations and subsequent secondary ion mass spectrometry measurements suggested the reduction of metal-vacancies and/or carbon impurity incorporation in the InGaN layers. (C) 2016 The Japan Society of Applied Physics
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| 8. |
- Knight, Sean, et al.
(författare)
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Electron effective mass in Sn-doped monoclinic single crystal beta-gallium oxide determined by mid-infrared optical Hall effect
- 2018
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:1
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Tidskriftsartikel (refereegranskat)abstract
- The isotropic average conduction band minimum electron effective mass in Sn-doped monoclinic single crystal beta-Ga2O3 is experimentally determined by the mid-infrared optical Hall effect to be (0.2846 +/- 0.013)m(0) combining investigations on (010) and ((2) over bar 01) surface cuts. This result falls within the broad range of values predicted by theoretical calculations for undoped beta-Ga2O3. The result is also comparable to recent density functional calculations using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional, which predict an average effective mass of 0.267m(0). Within our uncertainty limits, we detect no anisotropy for the electron effective mass, which is consistent with most previous theoretical calculations. We discuss upper limits for possible anisotropy of the electron effective mass parameter from our experimental uncertainty limits, and we compare our findings with recent theoretical results. Published by AIP Publishing.
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| 9. |
- Konishi, Keita, et al.
(författare)
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Comparison of O-2 and H2O as oxygen source for homoepitaxial growth of beta-Ga2O3 layers by halide vapor phase epitaxy
- 2018
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Ingår i: Journal of Crystal Growth. - : ELSEVIER SCIENCE BV. - 0022-0248 .- 1873-5002. ; 492, s. 39-44
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Tidskriftsartikel (refereegranskat)abstract
- Homoepitaxial growth of p-Ga2O3 layers by halide vapor phase epitaxy (HVPE) using O-2 or H2O as an oxygen source was investigated by thermodynamic analysis, and compared with measured properties after growth. The thermodynamic analysis revealed that Ga2O3 growth is expected even at 1000 C-degrees using both oxygen sources due to positive driving forces for Ga2O3 deposition. The experimental results for homoepitaxial growth on (0 0 1) beta-Ga2O3 substrates showed that the surfaces of the layers grown with H2O were smoother than those grown with O-2, although the growth rate with H2O was approximately half that with O-2. However, in the homoepitaxial layer grown using H2O, incorporation of Si impurities with a concentration almost equal to the effective donor concentration (2 x 10(16)cm (3)) was confirmed, which was caused by decomposition of the quartz glass reactor due to the presence of hydrogen in the system. (C) 2018 Elsevier B.V. All rights reserved.
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| 10. |
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| 11. |
- Masuda, Rui, et al.
(författare)
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Improvements in Optical Properties of (0001) ZnO Layers Grown on (0001) Sapphire Substrates by Halide Vapor Phase Epitaxy Using Thick Buffer Layers
- 2012
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Ingår i: Japanese Journal of Applied Physics. - : Japan Society of Applied Physics. - 0021-4922 .- 1347-4065. ; 51:3, s. 031103-
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Tidskriftsartikel (refereegranskat)abstract
- The optical properties of (0001) ZnO layers grown at 1000 degrees C on (0001) sapphire substrates by halide vapor phase epitaxy (HVPE) were investigated by various photoluminescence (PL) measurements. A layer grown with a H2O/ZnCl2 (VI/II) ratio of 20 on a 0.4-mu m-thick buffer layer exhibited a significant near-band-edge (NBE) peak blueshift and degraded internal quantum efficiency (eta(int)) due to residual compressive stress. Growth with a VI/II ratio of 600 diminished the NBE peak blueshift; however, deep level emission and a reduction of PL decay time (tau(PL)) were caused by point defects generated by excess O source supply. A layer without the NBE peak blueshift and deep level emission was realized by growth with a VI/II ratio of 20 and a buffer layer of 0.8 mu m. The eta(int) and tau(PL) for HVPE-grown layers could be improved to 4.1% and 122.8 ps by using the thick buffer layer and appropriate VI/II ratio.
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| 12. |
- Mock, Alyssa, et al.
(författare)
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Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic beta-Ga2O3
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:24
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Tidskriftsartikel (refereegranskat)abstract
- We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic beta-Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.
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| 13. |
- Murakami, Hisashi, et al.
(författare)
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Homoepitaxial growth of beta-Ga2O3 layers by halide vapor phase epitaxy
- 2015
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Ingår i: Applied Physics Express. - : Japan Society of Applied Physics. - 1882-0778. ; 8:1, s. 015503-
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Tidskriftsartikel (refereegranskat)abstract
- Thick high-purity beta-Ga2O3 layers of high crystalline quality were grown homoepitaxially by halide vapor phase epitaxy (HVPE) using gaseous GaCl and O-2 on (001) beta-Ga2O3 substrates prepared by edge-defined film-fed growth. The surface morphology and structural quality of the grown layer improved with increasing growth temperature. X-ray diffraction omega-rocking curves for the (002) and (400) reflections for the layer grown at 1000 degrees C had small full widths at half maximum. Secondary ion mass spectrometry and electrical characteristics revealed that the growth of high-purity beta-Ga2O3 layers with low effective donor concentration (N-d - N-a less than 10(13) cm(-3)) is possible by HVPE. (C) 2015 The Japan Society of Applied Physics
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| 14. |
- Nakahata, Hidetoshi, et al.
(författare)
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Investigation of halide vapor phase epitaxy of In2O3 on sapphire (0001) substrates
- 2021
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Ingår i: Journal of Crystal Growth. - : ELSEVIER. - 0022-0248 .- 1873-5002. ; 563
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the growth conditions on halide vapor phase epitaxy of In2O3 on sapphire (0 0 0 1) substrates was investigated. Only the most thermally stable phase c-In2O3 grows at growth temperatures of 400 to 1000 degrees C. The growth rate increased as the growth temperature increased up to 700 degrees C, and layers with rough surfaces and a preferred (100) orientation were grown. Above 700 degrees C, the growth rate became constant, the preferential orientation changed to (111), and layers with smooth surfaces were grown. At 1000 degrees C, the volume fraction of the (111)-oriented domains in the grown layer reached 99.0%, although there were in-plane twins rotated by 180 degrees. The growth rate also increased as the input partial pressure of the InCl or O-2 source gas was increased, and a high growth rate exceeding 10 mu m/h was found. The layer grown at 1000 degrees C was of high purity and incorporated no impurities other than Cl. Optical transmission measurements of this layer showed high optical transmittance at energies below the optical gap of 3.47 eV.
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| 15. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Defects and impurities in β-Ga2O3
- 2019
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Ingår i: Ultra-Wide Bandgap Semiconductor Materials. - : Elsevier. - 9780128154687 - 9780128172568 ; , s. 331-345
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 16. |
- Nguyen, Son Tien, et al.
(författare)
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Electron paramagnetic resonance and theoretical study of gallium vacancy in β-Ga2O3
- 2020
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 117:3
-
Tidskriftsartikel (refereegranskat)abstract
- Unintentionally doped n-type beta -Ga2O3 becomes highly resistive after annealing at high temperatures in oxygen ambient. The annealing process also induces an electron paramagnetic resonance (EPR) center, labeled IR1, with an electron spin of S=1/2 and principal g-values of g(xx)=2.0160, g(yy)=2.0386, and g(zz)=2.0029 with the principal axis of g(zz) being 60 degrees from the [001](*) direction and g(yy) along the b-axis. A hyperfine (hf) structure due to the hf interaction between the electron spin and nuclear spins of two equivalent Ga atoms with a hf splitting of similar to 29G (for Ga-69) has been observed. The center can also be created by electron irradiation. Comparing the Ga hf constants determined by EPR with corresponding values calculated for different Ga vacancy-related defects, the IR1 defect is assigned to the double negative charge state of either the isolated Ga vacancy at the tetrahedral site (V-Ga(I)(2-)) or the V-Ga(I)-Ga-ib-V-Ga(I) complex.
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| 17. |
- Schubert, Mathias, et al.
(författare)
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Phonon properties: Phonon and free charge carrier properties in monoclinic-symmetry ß-Ga2O3
- 2020
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Ingår i: Gallium Oxide. - Cham : Springer. - 9783030371524 - 9783030371555 - 9783030371531 ; , s. 501-534
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We present and discuss the complete set of infrared-active phonon modes in monoclinic-symmetry crystal modification gallium oxide (gallia, ββ-Ga2O3). The phonon mode set is obtained from a comprehensive analysis of generalized spectroscopic ellipsometry data in the farinfrared and infrared spectral regions investigating various n-type electrically conductive single crystal samples with different free electron volume density parameters cut under different orientations. The analysis of the ellipsometry data is performed using an eigendielectric displacement vector summation (EDVS) approach. In this approach, the effect of the free charge carriers onto the lattice modes of intrinsic ββ-Ga2O3 are removed by calculation. Density functional theory calculations are performed in the general gradient approximation and all phonon modes at the Brillouin-center and their displacement direction dependencies are obtained. Transverse and longitudinal optical phonon mode parameters polarized within the monoclinic plane as well as perpendicular to the monoclinic plane agree excellently between experiment and theory. We also present and discuss the directional limiting frequency parameters within the monoclinic plane, the shape and anisotropy of the reststrahlen band, and the order of the phonon modes in semiconductors with polar phonon modes and monoclinic crystal structure. We further present and discuss the effect of coupling of longitudinal optical phonons with free charge carriers, leading to longitudinal-phonon-plasmon coupled modes. We reveal that the coupled modes, which affect electric and thermal transport, change amplitude, frequency, and direction within the monoclinic plane as a function of free electron concentration. Finally, we show optical Hall effect measurements, and provide experimentally determined effective electron mass parameters in ββ-Ga2O3 for moderately-doped n-type samples.
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| 18. |
- Togashi, Rie, et al.
(författare)
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Effect of High NH3 Input Partial Pressure on Hydride Vapor Phase Epitaxy of InN Using Nitrided (0001) Sapphire Substrates
- 2013
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Ingår i: Japanese Journal of Applied Physics. - : Japan Society of Applied Physics. - 0021-4922 .- 1347-4065. ; 52:8
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the source gas supply sequence prior to growth and the NH3 input partial pressure (PoNH3) on the nucleation of InN islands during the initial stages of hydride vapor phase epitaxy on a nitrided (0001) sapphire substrate was investigated. The crystalline quality of the InN layer after subsequent lateral growth was also examined. When NH3 was flowed prior to growth, single-crystal hexagonal InN islands formed. When InN was grown with a higher PoNH3, the number of InN islands decreased remarkably while their diameter increased. The crystalline quality of InN grown on the hexagonal islands with a high PoNH3 significantly improved with increasing growth time. A strong PL spectrum was observed only from InN layers grown with a high PoNH3. It was thus revealed that an NH3 preflow and a high PoNH3 are effective for producing InN with high crystalline quality and good optical and electrical properties.
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| 19. |
- Togashi, Rie, et al.
(författare)
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High rate growth of In2O3 at 1000 degrees C by halide vapor phase epitaxy
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:12
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the first-ever growth of cubic-In2O3 at 1000 degrees C by halide vapor phase epitaxy (HVPE) was achieved, using gaseous InCl and O2 as precursors in a N-2 flow. The growth rates of In2O3 layers on (001) beta-Ga2O3 and (0001) sapphire substrates were 4.1 and 5.1 mu m/h, respectively, even at the high growth temperature applied, which are approximately half the growth rate of beta-Ga2O3 homoepitaxially grown by HVPE at 1000 degrees C. Theoretical thermodynamic analyses were also conducted, and results confirmed the growth of In2O3 at temperatures above 1000 degrees C by HVPE. The as-grown In2O3 layers were light yellow-green in color. The In2O3 layers grown on the (001) beta-Ga2O3 and (0001) sapphire substrates exhibited an optical absorption edge at about 370 nm, in addition to n-type conductivity with electron concentrations of 2.7 x 10(18) and 1.7 x10(18) cm(-3), and electron mobilities of 16.2 and 22.7cm(2)V(-1) s(-1), respectively. (C) 2016 The Japan Society of Applied Physics
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| 20. |
- Togashi, Rie, et al.
(författare)
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High rate InN growth by two-step precursor generation hydride vapor phase epitaxy
- 2015
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 422, s. 15-19
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Tidskriftsartikel (refereegranskat)abstract
- The increase of InN growth rate by a newly developed two-step precursor generation hydride vapor phase epitaxy (HVPE) was investigated for the preparation of freestanding InN and InGaN substrates. An elevated growth rate was achieved by the complete conversion of InCl generated in the first source zone to InCl3 in the second source zone, by the supply of additional Cl2. The growth rate reached 12.4 μm/h at a growth temperature of 600 °C, and the rate was observed to decrease above this temperature. Specular InN layers grown at 650 °C exhibited a sharp room temperature photoluminescence peak at 0.73 eV with a bulk electron concentration of 1.2×1018 cm−3.
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| 21. |
- Togashi, Rie, et al.
(författare)
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Thermal and chemical stabilities of group-III sesquioxides in a flow of either N-2 or H-2
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:12
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Tidskriftsartikel (refereegranskat)abstract
- The thermal and chemical stabilities of group-III sesquioxides (Al2O3, Ga2O3, and In2O3) were comparatively investigated at an atmospheric pressure at heat treatment temperatures ranging from 250 to 1450 degrees C in a flow of either N-2 or H-2. In a flow of N-2, the thermal decomposition of alpha-Al2O3 was not observed at the temperatures investigated, while the decompositions of beta-Ga2O3 and c-In2O3 occurred above 1150 and 1000 degrees C, respectively, with no generation of group-III metal droplets on the surfaces. In contrast, the chemical reactions of alpha-Al2O3, beta-Ga2O3, and c-In2O3 began at low temperatures of 1150, 550, and 300 degrees C in a flow of H-2. Thus, the presence of H-2 in the gas flow significantly promotes the decomposition of group-III sesquioxides. The order of thermal and chemical stabilities (alpha-Al2O3 amp;gt;amp;gt; beta-Ga2O3 amp;gt; c-In2O3) obtained experimentally was verified by thermodynamic analysis, which also clarified dominant decomposition reactions of group-III sesquioxides. (C) 2016 The Japan Society of Applied Physics
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| 22. |
- Togashi, Rie, et al.
(författare)
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Thermal stability of beta-Ga2O3 in mixed flows of H-2 and N-2
- 2015
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Ingår i: Japanese Journal of Applied Physics. - : Japan Society of Applied Physics. - 0021-4922 .- 1347-4065. ; 54:4, s. 041102-
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of beta-Ga2O3(010) substrates was investigated at atmospheric pressure between 250 and 1450 degrees C in a flow of either N-2 or a mixture of H-2 and N-2 using a radio-frequency induction furnace. The beta-Ga2O3 surface was found to decompose at and above 1150 degrees C in N-2, while the decomposition of beta-Ga2O3 began at only 350 degrees C in the presence of H-2. Heating beta-Ga2O3 substrates in gas flows containing different molar fractions of H-2 demonstrated that the decomposition was promoted by increasing the H-2 molar fractions. Thermodynamic analysis showed that the dominant reactions are Ga2O3(s) = Ga2O(g) + O-2(g) in N-2 and Ga2O3(s) + 2H(2)(g) = Ga2O(g) = 2H(2)O(g) in a mixed flow of H-2 and N-2. The second-order reaction with respect to H-2 determined for the mixed flows agrees with the experimental results for the dependence of the beta-Ga2O3 decomposition rates on the H-2 molar fraction.
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| 23. |
- Tojo, Shunsuke, et al.
(författare)
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Influence of high-temperature processing on the surface properties of bulk AlN substrates
- 2016
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Ingår i: Journal of Crystal Growth. - : ELSEVIER SCIENCE BV. - 0022-0248 .- 1873-5002. ; 446, s. 33-38
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Tidskriftsartikel (refereegranskat)abstract
- Deep-level luminescence at 3.3 eV related to the presence of Al vacancies (V-Al) was observed in room temperature photoluminescence (RT-PL) spectra of homoepitaxial AlN layers grown at 1450 degrees C by hydride vapor-phase epitaxy (HVPE) and cooled to RT in a mixture of H-2 and N-2 with added NH3. However, this luminescence disappeared after removing the near surface layer of AlN by polishing. In addition, the deep-level luminescence was not observed when the post-growth cooling of AlN was conducted without NH3. Secondary ion mass spectrometry (SIMS) studies revealed that although the point defect density of the interior of the AlN layers remained low, the near surface layer cooled in the presence of NH3 was contaminated by Si impurities due to both suppression of the surface decomposition by the added NH3 and volatilization of Si by decomposition of the quartz reactor walls at high temperatures. The deep-level luminescence reappeared after the polished AlN wafers were heated in presence of NH3 at temperatures above 1400 degrees C. The surface contamination by Si is thought to generate V-Al near the surface by lowering their formation energy due to the Fermi level effect, resulting in deep-level luminescence at 3.3 eV caused by the shallow donor (Si) to V-Al transition. (C) 2016 Elsevier B.V. All rights reserved.
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| 24. |
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| 25. |
- Yoshida, Kento, et al.
(författare)
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Dependence of thermal stability of GaN on substrate orientation and off-cut
- 2019
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 58
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of +/- c- and m-plane GaN substrates and its dependence on the m-plane GaN off-cut angle were investigated at and above 1200 degrees C at atmospheric pressure in flowing N-2 with and without added NH3. It was clarified that decomposition of the +c-plane GaN surface is promoted by the addition of NH3, while decomposition of the -c- and m-plane GaN surfaces is suppressed by added NH3. It was found that -c- and m-plane GaN substrates can be heated at 1300 degrees C with an added NH3 input partial pressure of more than 0.2 atm, which is 100 degrees C higher than for +c-plane GaN substrates. Nevertheless, decomposition of m-plane GaN substrates became noticeable with increase in the off-cut angle of the substrate. It was revealed that the decomposition was better controlled by using m-plane GaN substrates with an off-cut towards [000 (1) over bar] than towards [0001]. (C) 2019 The Japan Society of Applied Physics
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